As disclosed in U.S. Pat. Nos. 4,573,300 and 6,164,024, module glazing panels are used with a framing grid of purlins and rafters to form a wall, an overhead or roofing structure such as for skylights, covered walkways, pool enclosures, building atriums, greenhouses, etc. Glazing panels generally have light transmission properties to allow light to pass through the structure to illuminate interior regions covered by the glazing panels. The glazing panels disclosed in the above-identified patents as well as those made by other manufacturers are provided with upstanding seam flanges which extend along the side edges at the ends of the panels for being connected to one another with connectors. As disclosed in U.S. Pat. No. 4,573,300, the upstanding seam flanges were provided with projecting saw teeth and batten type joining connectors having internal saw teeth which were pushed down over the saw teeth on the seam flanges to snap fit the saw teeth together to join the adjacent panels by means of the batten only. U.S. Pat. No. 6,164,024 discloses the use of improved joining or retention clips made of metal which are used to join adjacent seam flanges together as well as cooperating with a batten which covers the seam flanges and clips. The retention clips have top flanges that provided the clip with improved holding power to hold the panels against becoming loose and sliding out from the glazing panel system during high wind loading of the glazing panel system. More specifically, high winds flowing across very large surfaces exert negative uplift forces on the panels which tend to separate the panels from one another and the retention clips as well as the battens are required to retain the glazing panel structure intact despite such forces. This vacuum or negative pressure caused by high winds flowing over the glazing panels with a pressurized interior of the building can cause the glazing panels to be pulled off unless the clips and panels are sufficiently strong to resist the forces being generated.
The glazing panels tend to bow upwardly under negative wind loads due to high velocity wind flow across the outer external major surfaces of the glazing panels. A positive air pressure on the interior surface also may contribute to this bowing of the glazing panels. Testing shows that as the adjacent glazing panels bow, the lower interior ends of the glazing panels separate and form a larger gap therebetween. In the glazing panel systems without a retention clip, the enlarging space between these lower interior ends of the glazing panels tends to break the engagement of the toothed surfaces on the upstanding seam flanges and depending legs of the inverted channel seam covering connector which covers the seam between adjacent panels. These uplift loads then tend to pop the U-shaped connector up as the teeth of the upstanding seam flanges separate from the teeth on the legs of the inverted channel connector.
When a retention clip is present as well as the inverted channel connector, as disclosed in U.S. Pat. No. 6,164,024, the top ends of the seam flanges pivot or hinge under the clip top flange as the panels increase in their amount of bowing and the gap at the lower ends of the panels increases due to increase bowing of the panels. The angle defined between adjacent upstanding seam flanges hinged at their upper ends increases with increased bowing of panels and also the gap increases between lower interior ends of the glazing panels. At sufficiently high uplift loads, e.g., exceeding that for which the glazing panel system is rated, the outer connector may flex outwardly and then separate its teeth from the teeth on the upstanding seam flanges resulting in the seam covering connectors being disconnected from the seam flanges and the upper ends of the glazing panels sliding outwardly from the top flanges of the retention clips. Thus, at loads greater than that for which the glazing panel system is rated, the glazing panels separate and may be lifted from the purlins and rafters resulting in a failure of the glazing panel retention systems.
Various codes have been adapted, particularly in hurricane designated areas, to subject windows, skylights and other glazing panel systems to uplift loads and negative forces which might be encountered during a hurricane or the like. One such standard is South Florida Building Code (SFBC). United Laboratories Standard “UAL 580” sets forth three different standards or ratings for glazing panel systems of 90, 60 and 30. To meet the UAL 580 standard or rating 90 the glazing panels are subjected and must resist an uplift wind load of 105 pounds per square foot (psf). For the UAL 580 standard 60, the glazing panel system must resist an uplift load of 75 psf. The UAL 580 standard 30 tests the glazing panel systems with an uplift load of 45 psf. Manifestly the present invention is not limited to any particular standard but these standards are set forth only by way of example; other standards that are currently use such as those set forth by the American Society of Civil Engineers, ASCE-7, ASTME 1996 and IBC.